Phased arrays create beamed radiation patterns in free space to allow the formation of selective communication channels. A phased array is formed by placing a plurality of antennas in a grid pattern on a planar surface where these antennas are typically spaced ½ of the wavelength of the radio frequency (RF) signal from one another. The phased array can generate radiation patterns in preferred directions by adjusting the phase and amplitude of the RF signals being applied to each of the antennas. The emitted wireless RF signals can be reinforced in particular directions and suppressed in other directions due to these adjustments. Similarly, phased arrays can be used to reinforce or select the reception of wireless RF signals from preferred directions of free space while canceling wireless RF signals arriving from other directions. The incoming RF signals, after being captured by the phased array, can be phase and amplitude adjusted and combined to select RF signals received from desired regions of free space and discard RF signals that were received from undesired regions of free space. The wireless beam is steered electronically to send and receive a communication channel, thereby eliminating the need to adjust the position or direction of the antennas mechanically.
A phased array requires the orchestration of the plurality of antennas forming the array to perform in unison. A corporate feed network provides the timing to the phased array by delivering identical copies of an RF signal to each of the plurality of antennas forming the phased array. A uniform placement of the plurality of antennas over a planar area defines the phased array as having a surface area that extends over several wavelengths of the carrier frequency of the RF signal in both of the X and Y directions. For example, a phased array with 100 antennas arranged in a square planar area would have edge dimension equal to 5 wavelengths of the RF carrier frequency in each direction.
The corporate feed network can be a passive or active tree network that extends its branches to the antennas of the phased array that cover this surface area. Networks that accomplish this form of distribution are known as a binary tree distribution (for linear array) and H-tree distribution (for planar array) networks. A binary tree can be a 1:N distribution network that is formed using a binary partitioning. A source signal is matched to an input/output (I/O) port of a transmission line. The end of the transmission line is split to two equal length transmission lines where certain impedance matching conditions must be met at the split. This junction comprising this split is called a power divider. Theoretically a power divider is lossless, reciprocal and matched at all three ports, but is difficult to construct. In practice, the power divider can be made lossy at the expense of maintaining the divider reciprocal and matched. The ends of the two equal length transmission lines are each split with power splitters' and transmission line segments. The process of splitting each added transmission line continues until the number of branch tips (I/O ports) of the passive tree equals N (a power of 2). The antennas can be coupled to the branch tips. Each of the N branch tips must be properly terminated.
Such a binary partitioned network insures that the summation of the lengths of the transmission lines coupling the I/O port of the first transmission line to each of the branch tips in a corporate feed network is equal in length. Thus, the flight time of a signal sourced at this I/O port along any of these paths to each of the plurality of branch tips would be the same. This theoretically eliminates any phase variation of that signal when multiple copies of the signal arrive at all of the branch tips. These are the signals used to orchestrate the plurality of antennas in unison. Once the RF signal arrives at every antenna from the network, the phase/amplitude of the RF signal is adjusted locally at each antenna to create the desired radiation pattern described earlier.
Since the power dividers are reciprocal, the corporate network can also be used to transfer signals from the antennas that are coupled to the branch tips and combine these signals at the I/O port of the first transmission line. Corporate feed networks are used to extract desired RF signals captured by the antennas of the phased array from different regions of free space; the phase/amplitude of the received RF signal is adjusted locally at each antenna to select a desired radiation pattern from free space.
Conventional phased arrays use corporate feed networks to transport RF signals to and from the antennas. The corporate feed network propagates all these high frequency components of the RF signal from a single source to all of the individual antennas of the phased array. Some of the frequency components of the RF signal will experience impedance mismatch at the power splitters causing reflections that leads to the distortion of the signal. The high frequency signal content of the RF signal suffers skin effect losses in the transmission lines, which can further degrade the quality of the RF signal. In order to operate at high frequencies, the transmission lines need to have high quality, low-dispersion properties. To minimize losses in this network and to insure that proper impedance matching occurs within this network is a challenge. A system to meet this challenge is costly since it requires all components of the system to have well-controlled impedances to minimize reflections at the splitters and to have low loss characteristics to prevent signal degradation.
It is understood that the distribution of the RF signal over the corporate feed network to and from a plurality of antennas is a difficult challenge due to the loss of signal and mismatch issues. Such a system incurs a higher cost of manufacturing to construct the circuit board and connectors in an attempt to reduce these concerns.